The present invention relates to a surface acoustic wave device for use in wireless communications equipment and the like and method of manufacture thereof.
FIG. 23 is a cross-sectional view of a conventional surface acoustic wave device (hereinafter SAW device). Referring to FIG. 23, a description will be given below on the method of manufacture of the conventional SAW device.
First, interdigital transducer electrodes (IDT electrodes) 101 and connection electrodes 102 are formed by forming vacuum deposited aluminum film on a disk (wafer) of piezoelectric material followed by exposing with a pattern of predetermined configuration and developing. Subsequently, acoustic absorbers 103 are formed by coating a silicone resin on both sides of the IDT electrodes 101 by screen printing and heat treatment. In this way, a number of surface acoustic wave elements 105 (SAW elements) are collectively formed on the wafer. Subsequently, the wafer is diced into individual SAW elements 105.
Next, a SAW element 105 is secured with adhesive 108 in a package 107 having external terminals 106, and the external terminals 106 and connection electrodes 102 are electrically connected with thin metal wires 109. Subsequently, opening of the package 107 is sealed with a lid 110.
When the acoustic absorbers 103 are formed by screen printing in this manner, the dimensional accuracy is poor and also their cross sections become dome-like due to drips caused by flow of the resin, thus suffering from the upper surfaces becoming curved and difficulty in forming with a uniform height.
Furthermore, when mounting the SAW element 105 in the package 107, as the SAW element 105 is transferred by sucking its surface with a vacuum chuck, there is a difficulty in sucking because the top surfaces of the acoustic absorbers 103 are curved and their heights are different. In addition, piezoelectric substrate 100 may incline relative to the bottom surface of the package 107 thus presenting a possibility of causing mounting failure.
FIG. 24 is a cross-sectional view of another conventional SAW device. While thin metal wires 109 connect the connection electrodes 102 and the external terminals 106 in the conventional SAW device of FIG. 23, in another conventional SAW device shown in FIG. 24, projecting electrodes 111 (bumps) make the connection.
In this case, too, there is a possibility of causing connection failure when the heights of the acoustic absorbers 103 are non-uniform and are greater than the bumps 111.
The present invention addresses the above issues and aims at providing a SAW device that can prevent mounting failure when mounting a SAW element in a package.
In order to attain this object, the SAW device of the present invention comprises a package having an external terminal, a SAW element housed in the package, and a lid for sealing opening of the package, wherein the SAW element further comprises on the surface of a piezoelectric substrate at least an IDT electrode, a connection electrode electrically connected to the IDT electrode, and an acoustic absorber formed on the outside of the IDT electrode, that is, on an end portion of the piezoelectric substrate, in a manner such that its top surface is parallel to the main surface of the piezoelectric substrate. As the surface of the acoustic absorber is parallel to the main surface of the piezoelectric substrate in this way, and as the top surface of the acoustic absorber is a plane, it is easy to suck the SAW element with a vacuum chuck when mounting in a package and it is possible to securely mount it at a predetermined position of the package.